Associate Professor Adjunct

Research Interests

Research Organizations

Research Summary

In the very crowded inner environment of a cell, most macromolecules function in the form of complexes, many being described as “molecular machines.” To understand the machines’ structures and structural changes that occur during the working cycle, we employ cryo-electron microscopy (cryo-EM) to visualize molecules as “single particle” or ordered functional assemblies. The micrographs are analyzed by computational image processing to reveal the structure and conformational variations of the molecules. We then combine the structural information with data from accompanying biophysical and biochemical techniques to elucidate the mechanisms of these large macromolecular machines. Our current research focuses on two topics: The first one is the mechanisms and regulation of exosome-mediated RNA processing and degradation. We use cryo-EM to capture clear snapshots of the entire exosome complex binding with its different cofactors in their various working states to better understand the molecular mechanism of RNA quality control in eukaryotic cells. The second one is the regulation of microtubule dynamics at the cell cortex. Using cryo-EM, we study the interactions between microtubule’s dynamic plus ends and other subcellular structures and assemblies at the cell cortex in order to understand microtubule’s roles in essential cellular processes such as differentiation and migration.

Extensive Research Description

In the very crowded inner environment of a cell, most macromolecules function in the form of complexes, many being described as "molecular machines." To understand the machines' structures and structural changes that occur during the working cycle, we employ cryo-electron microscopy to visualize molecules as "single particle" or ordered functional assemblies. The micrographs are analyzed by computational image processing to reveal the structure and conformational variations of molecules. We then combine the structural information with data from accompanying biophysical and biochemical techniques to elucidate the mechanisms of these large macromolecular machines. Our current research focuses on (1) RNA degradation and (2) microtubule dynamics.

The mechanisms and regulation of exosome-mediated RNA processing and degradation.

Post-transcriptional processing is a major regulatory step in the expression of eukarytoic genes. Almost all RNA transcripts undergo maturation pathways such as splicing,

3'– end processing, or 5'–end capping before becoming functionally competent. The maturation process is continuously monitored by RNA quality control systems, which selectively degrade aberrant RNA species. The exosome complex of 3'-to-5' exoribonucleases plays a key role in these quality control processes. It is involved in both the 3'-end processing and degradation of RNA species in the nucleus and cytoplasm. In its role as a crucial RNA processing and degradation machine, the exosome works in conjunction with a whole host of ancillary cofactors in a highly regulated manner. To fully understand the mechanisms and regulation of this important cellular machinery, we utilize electron microscopy and single particle reconstruction techniques to reveal the structure of the exosome in complex with its different cofactors, both with and without the RNA substrate.

The regulation of microtubule dynamics at the cell cortex.

Microtubules are the primary cytoskeletal components defining cell shape. They function together with the actin network, cell membrane, and other cellular structures at the cell cortex in cell polarization, cell migration, and cytokinesis. Although each of these individual systems has been studied intensively, the interaction and coordination among them—especially those between microtubules, actin filaments, and cell membranes—are just beginning to be appreciated. Most microtubules extend their plus ends into the cortical region of the cell. These ends show astoundingly dynamic behavior by switching stochastically between states of growth and shrinkage, termed the dynamic instability of microtubules. We are now using cryo-electron microscopy to study the structural basis of the regulation of microtubule dynamicity at the cell cortex via its interactions with other subcellular structures and assembly systems, such as the actin network.

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